Electrical energy is sometimes generated by attaching a generator or alternator to the frame of a vehicle and coupling the rotor of the device to the axle of the vehicle. As the vehicle axle rotates the device rotor also rotates thereby generating the desired electrical energy. Such power generating devices are used in the railroad industry and take many different forms. A serious objection to most of these devices is that they are coupled to the railroad car axle in such a way that the bearing end cap of the axle must be either temporarily removed and replaced or a different end cap substituted. The reason that this is undesirable is that this disturbs the axle bearing when removing the bearing end cap and requires the skill of a workman that is specifically trained in this procedure requiring resources and equipment normally found in central work shops necessitating sending each railroad car that is to be retrofitted with one of these power generating devices to the central work shop for installation. It is, therefore, desirable to couple the power generating device to the railroad car axle without disturbing the bearing end cap so that the installation can be accomplished in the field thereby reducing service disruptions and equipment requirements.
A power generating device and axle coupling of the related art is disclosed in French patent number FR2 624 818. This device is secured to the truck of the railroad car by means of bolts that are threaded into the vehicle frame. The rotor of the device has a drive shaft that is held in alignment with the vehicle axle. A coupling disc having three circular cutouts formed in its periphery is attached to the end of the drive shaft so that the three bolts holding the bearing end cap in place are positioned so that each of their heads is located within one of the three cutouts. As the vehicle axle rotates, the bolt heads engage the edges of the cutouts and cause the coupling disc and attached drive shaft to rotate. Due to the somewhat loose coupling of the railroad car frame to the vehicle axle, the car is permitted to move relative to the axle during normal operation. This movement can be up to 0.5 inch in all directions perpendicular to the axle and up to 0.25 inch in the axial direction. As a result of this rather substantial amount of possible relative movement, the coupling disc can be jammed against one of the bolt heads thereby damaging the coupling disc or the bolt head, or the coupling disc can completely disengage the three bolt heads causing the device to become inoperable.
What is needed is a coupling that can engage one or more of the bolt heads for driving the rotor of the alternator while having the ability to accommodate the possible extreme lateral and axial movement of the car with respect to the axle.